our report tonight from our chief science correspondent robert bazell. >> it is beautiful though. >> fabulous. >> reporter: john shoemaker and his wife donna remember seven years ago when he learned he had prostate cancer. >> initially it was, oh, my god, you know, am i going to live? what's going on? >> i was pretty upset. i was crying. i was hysterical. >> reporter: since then john has gotten no treatment, and he's perfectly healthy. his doctor watches the tumor in a routine called active surveillance. a new test may help determine when that is a good option. it measures 17 genes and should allow more men and their doctors to know whether it is safe to go untreated. john, a retired computer executive was scheduled for surgery. he then visited dr. peter carol who has long argued while prostate cancer can be deadly, often it is not. so treatment that can cause side effects including impotence and incontinence is not always necessary. >> how many men do you think were treated with surgery or radiation who could have lived to a long, healthy life without it. >> a large, large, very lar